Amplifier system



Aug. 3 1926.

P. J. WALSH AMPLIFIER SYSTEM Filed Feb. 24, 1925 QC. Saw-ca INVEN TOR Phi/p J. Wd/sh BY ms ATTORNEY Patented 9mg. 3; 1926.

UNITED STATES PHILIP JOHN WALSH, OF SAN FRANCISCO, CALIFQRKIA.

AMPLIFIER SYSTEM.

Application filedlebruary 24, 1925. Serial No. 11,371.

This invention relates to a system for amplifying weak electrical impulses, such for example as are received in radio re ceiving systems.

It is one of the objects of my invention to provide a scheme for a large degree of amplification in each stage, by the'aid of relatively few parts, that are simple to assemble, and also to operate.

I show my invention as applied to thermionic vacuum tube amplifiers, and it is a further object of my invention to mak it possible to operate relatively few tubes for a'desired degree of amplification. In this connection, my invention relates to a novel scheme of connections whereby these useful results are obtained.

As the description proceeds, it will become apparent that my invention has many other a vantages. The novel features of .construction and operation upon which these advantages rest are set forth in the appended claims. The invention, however, may best be understood from a detailed description of one embodiment of my invention, illustrated in the accompanying drawings. Although but one embodiment is specifically described, it is evident that many other forms may be devised, as maybe ascertained from the breadth of said claims.

Referring to the drawings:

The single figure is a wiring diagram of one form of my invention.

In the resent instance I show my invention applied to a radio receiving system having an absorbing circuit includingthe antenna 1, loading inductance coil 2, and a ground connection 3. A conventional tuned circuit is shown as coupled to the coil 2, and as consistin of a coil 4, and a variablecondenser .5. h electromotive forces due to the received electrical energy and available at the terminals of coil 4 are caused to affect an amplifier, such as the three electrode thermionic tube 6. This tube has a heated filament 7, serving as a source of electronic emission; a plate or anode 8' to which the electrons are caused to flow through the intervening tube space; and a control elec- 'trode or grid 9, that is arranged toaffect the electric condition of the space in the tube 6, and thereb the flow of electrons between the electro es 7 and 8. The principle of operation" of such tubes is now quite well known. The impulse to be amplified is caused to affect the potential difference between the filament 7 and grid 9, and variations in this potential difference cause corresponding larger variations in the resistanceof 'the space between filament 7 and plate 8, to the flow of the electrons. These Variations in resistance in turn cause varia tions in th current flow of associated circuits, which will hereinafter be described.

The filament 7 in this instance is shown as heated by the aid of a transformer 10 arranged to be supplied with energy from a commercial source. The heating current however can be secured if necessary in other ways.

, One of the important features of my inventionresides in the manner in which. the output current is supplied for the output circuit amplifier 6. A source 11 of direct current is shown, which is connected between the plate 8 and the filament'7; the output circuit of which the resistance is varied by the operation of the control electrode 9 can thus be traced: from the plate 8, an inductance coil 12, loading coil 13, positive terminal of source 11, negative terminal of source 11, another loading coil 14, the centre tap 15 of secondary of transformer 10, to the filament 7. The'direct' current source 11 supplies the necessary difference of potential between the two electrodes 7 and 8 in the evacuated receptacle so that the electrons emitted from filament 7 are impelled under the influence of the electric field, to the plate electrode 8.

By proper choice of the source 11, and of the loading coils 13 and 14, it 'is'possible so to arrange matters that the total current delivered by the source remains substantially constant, independently of the resistance offered by the output circuit just traced. This circuit is however but one of a plurality of paths offered to the current from source 11, and it is one of the purposes of the invention to vary the relative conductivities of these paths in accordance with the impulses amplified. In the present instance I show but one other path for the flow of the current from source 11. This path'includes the output'circuit of another amplifier tube 15, and may be traced as follows: from ,the positive terminal of source 11, coil 13, an inductance coil 16 coupled to coil 12, plate 17 of. tube 15, through the space of tube 15 toi filament 18, center tap 31 of the secondary of heating transformer 19, connection 20, coil 14,

vice versa.

are being received, the resistance 0 to the negative terminal of source 11. The

resistance of this branch to the source current is controlled by the grid electrode 21 interposed between the filament 18 and plate 17. v

The grid potential is controlled by the instrumentalities that will be described, in such manner that this parallel path has a relatively low resistance while. that including amplifier 6 has a high impedance, and

It is the difference in the current flow in these two paths that is used as the resultant output current.

This difference can be measured inseveral ways; for example, a coil 22 may be arranged to be coupled inductively to both coils 12 and 16, in such manner that these two latter coils affect coil 22 oppositely. This is indicated by the oppositely directed arrows 23 and 24.' The terminals of coil 22 are connected to succeeding stages or to any other form of translating device;

. I shall now describe how the resistances of the two paths are oppositely varied in response to the receipt of the impulses that are amplified. The grid 9 has in series therewith a potentiometer device, consisting of a battery 25, a resistance 26 connected across the battery, and a variable tap 27 leading to the condenser 5. The negative terminal of battery 25 is connected to the grid. It is seen that by varying the position of tap 27, it is possible to vary to some extent the relative potentials of the grid 9 and filament 7. Since the amount of space current flow is a direct function of this potential difference, it is possible by proper adjustment, to set the tap 27 so that when no im ulses that path including tube 6 may be readily determined.

Substantially the same arrangement is provided for the tube 15, there being a attery 28, bridged by a resistance 29, and having a variable tap 30. The negative terminal of battery 28 is connected to the grid 21. The circuit between grid 21 and filament 18 also includes the center tap 31,

and a tuned 'radio frequency circuit 32, including a coil 33 and a variable condenser 34: bridged across the coil. j This coil 33 is coupled, as indicated by arrow 35, to the coils 12,16, and 22, and the degree of this coupling can preferably be varied. The tap 30 on resistance 29 is preferably so adjusted relatively to that of tap 27 on resistance 26, that the effects of the currents in coils 12 i and 16 cancel each other, and their combined large coils 12 and 16. In case however there are more turns in coil 12 than in' coil 16, the grid potentials are .so fixed that less current flows through coil 12 and more through coil 16, the combined ampere-turns in each coil being again equal to produce substantial magnetic neutralization. It is thus seen that when no impulses are being received, there are merely unvarying currents flowing in the ,two paths, there is no appreciable magnetism affecting coil 22 or coil 33, and no currents are induced therein.

Now let it be assumed that an impulse is received which causes an electromotive force to be induced across the terminals of coil 4; in the present instance this electromotive force would vary at a radio frequency rate, but the principle is the same for other rates also. WVhile this electromotive force is such that the upper terminal of coil Iris increasingly negative, the current through coil 12 is then decreasing, due to the corresponding increased resistance of the space path in tube 6. Due to the fact that source 11 is a constant current one, the current through coil 16 is correspondingly increasing. .The result is that this coil now begins to overpower coil 12, and the magnetism coupling coils 16, 12, 22 and 33 is increasing'in one direction. This increase causes an electromotive force to be induced in both coils 22 and 33; coil 22 immediately affects the translating device, while coil 33 is so connected ence in current flow in the two coils 12 and 16.

The process of accentuating the difference in current flow, due to the'inductive coupling of coil 33 with other elements of the system, is controlled to some extent by the degree of coupling of coil 33 with the other coils. This can be so adjusted that there is no instability 'of.the system. Furthermore the elements of the system are designed for radio frequency operation so that they may respond without appreciable lag to the signaling impulses.

It is also to be understood that the electric and magnetic actions of the coils and their associated circuits are so dovetailed and complex that it'is not considered advisable to attempt a detailed theoretical exposition. The general efi'ects, however, as stated heretofore, is to vary in opposite directions, the two paths for the constant current from source 11; and the load circuit including coil 22 is made to respond to this difference. The difference as a matter of fact is greatly increased by the coupling of the input circuit of tube 15 with the output circuit of tube 6.

The action of the circuits has been outlined only for the condition when the upper terminal of coil 4 is increasingly negative;

grid 21 as to increase the resistance of that path which includes tube 15. The net result is that the difference in the two currents is again accentuated, and in coil 22 there is induced an electromotive force of opposite polarity as compared with that induced when the current in coil 12 was decreasing. The load circuit electromotive force thus faithfully follows the changes in'the electromotive force across coil 4. By proper design and adjustment of the parts, there will be sufiicient variation of current flow to enable a loud speaker to be operated fromcoil 22.

In the present instance, the output circuit connects to a usual form of thermionic detector 37 having a heated filament 38, a control electrode 39, and a plate or anode 40. The grid or input circuit connects across a variable condenser 41, which in conjunction with coil 22, forms a tuned circuit for the radio frequency. The input circuit includes the, grid bias battery 42, its associated variable resistor 43, the usual grid condenser 44 and high resistance leak 45. The principle of operation of the condenser and leak is now well-known and need not be detailed except to point out that the arrangement serves to integrate the radio frequency impulses, and in the output circuit, the audio frequency signals become translated into audio frequency variations in the current flowing therein.

Although it is possible directly to affect a translating device, such as the phones 46, by the output current, I show an, audio frequency amplifier system operating on the principle alread described. For this purpose, a source 4% is used, which supplies a constant current to two paths in parallelone'includilrg the output circuit of detector 37, and the-other, the output circuit of another audio frequency amplifier tube 48.

The output circuit of tube 37 also includes a-coil49 which is coupled to a similar coil 50 in the output circuit of tube 49. As before, these two coils oppose each other, and

the negative bias of each of the two grids- 39 and 51is made such that substantial magnetic neutralization exists between these two coils while no signals are being received. Since audio frequency 'currents are being dealt with here, it is feasibl to use a magnetic core 52 on which all of the coils may be placed. The load circuit including the phones 46 is coupled to both coils by the aid of coil 53, whereby this coil is made responsive to the difference in the ampere turns produced in the two' shunt circuits. The path including tube 48 has its impedance controlled by the aid of thegrid circuit which includes a coil 54. This coil is adjustably coupled to the coils-50 and 49 by being movably mounted on core 52. In other respects the audio frequency system is similar to the radio frequency system already described. The potential of grid 51 relative to the filament55 is varied simultaneously oppositely tothatof grid 39 relative to filament 38, as the signals .are received. This results in a large variation in the magnetism that threads core 52. This variation in turn *causes' a corresponding flow ofcurrent in the coil 53 and in the loud speaker 46.

As before, the adjustment of the coil 54 with respect to the coils 49 and 50 provides for a control of the building up action that takes place between the two coils 50 and 49. Nevertheless, the amplifying action can be made suflicient to produce a large intensity of signal well within the range of stable operation.

I claim: 7 1. In a system for amplifyingv electrical impulses, having a source arranged to provide substantially a constant current, and a pair of paths for the current, the process which comprises magnetically coupling the two paths, varying the impedance of one path in accordance with the impulses to be amplified, and oppositely varying the impedance of the other path in accordance with the variations in the magnetismvin the coupling of the two paths.

2. In a system for amplifying electrical impulses, a source arranged to provide substantially a constant current, means forming pulses to be amplified, a source of constant current arranged to provide the space current for said device, a second electron c emission device also supplied with space current from the same source, an nductance.

coil in each of the space current 'aths, the coils being coupled and arranged to have opposite ma netic"eifects, another coil also coupled to. t ehther two and arranged to effect the second electronic emission device in accordance with the variations in magnetism produced jointly by the first two coils and in such manner that the impedance of the second device is oppositely varied as regardsthe first device, and a load circuit also coupled to the two coils.

'4. The system as set forth in claim 3, in which the coupling between the first two coils and that coil which affects the second electronic emission device is variable, Whereby the. extent of dependence of the second device on the first one may be varied;

5. In a system for amplifying electrical impulses, an electronic emission device,

causes the. entire variation in the impedance of the second device, and in an opposite sense, a common source of space current for both devices, and means whereby the dif ference in the two space currents is utilized as the amplified impulse.

In witness whereof I have hereunto set my hand.

PHILIP JOHN WALSH. 

